1. Field of the Invention
The present invention relates to a device that detects an overcurrent attributable to a short-circuit abnormality occurring in an electrical drive control system and a detection method adopted in the device.
2. Description of Related Art
An electrical drive control system of a hybrid electric vehicle or an electric vehicle achieves variable-speed drive of an AC motor by utilizing a power conversion device constituted with a voltage inverter (referred to simply as an “inverter” in the following description of the invention) which converts a DC voltage to an AC voltage. Such an inverter is equipped with an fault detection circuit for detecting, for instance, an overcurrent.
If, for instance, an output ground fault attributable to electrically conductive foreign matter, or line-to-line short-circuit or phase-to-phase short-circuit attributable to a dielectric breakdown occurring inside the motor connected to the electrical drive control system occurs on the output side of the inverter in the electrical drive control system, the amplitude of a current output from the inverter will increase quickly, and an overcurrent state comes up in the electrical drive control system, in which a current exceeding the maximum rated continuous current or the short-time rated current of the transistors constituting the inverter flows.
The inverter disclosed in Japanese Laid Open Patent Publication No. S 61-98188 determines that an overcurrent has occurred upon detecting a current exceeding a predetermined threshold value.